Solvent for Separating Acid Gas Components from Technical Gases

ABSTRACT

The invention relates to the use of a liquid, containing 0.1 to 100% of an amine or several amines of formula H 2 N—CH 2 (CHR 2 ) x —(OCH 2 (CHR 3 ) y ) z —OR 1 , where R 1 ═C 1  to C 6  alkyl, R 2 ═H or CH 3 , R 3 ═H or CH 3 , x=0 to 3, y=0 to 3, z=0 to 10 and 0 to 99.9% of any further solvent including piperazine and/or water for separating acid gas components from technical gases.

The invention relates to a solvent required to separate sour gas components from technical gases and suited for a scrubbing process which is performed to remove sour gas components from a technical gas bearing impurities, with the aid of a liquid, the said liquid being subsequently regenerated and recycled in a closed loop.

A large number of separation methods are known in order to remove sour gas components from technical gases with the aid of solvents. A clear distinction is drawn between physically acting solvents and chemically acting solvents. Chemically acting scrubbing agents are capable of efficiently removing sour gas components at high loads, even at low to medium sour gas partial pressures (e.g. 0.1 to 2 bar). Higher sour gas partial pressures (e.g. >2 bars) permit the use of physically acting solvents at a higher sour gas content of the solvent, such that the physically acting solvent has a real benefit under these conditions.

The state-of-the-art removal of sour gas components from technical gases with the aid of chemically acting solvents is constituted, for example, by the MDEA scrubbing process which uses, for example, a solvent with a 50% by wt. solution of methyldiethanol amine and water for sour gas removal. This amine concentration is in line with the present state of technology, the concentration best suited for the removal of large sour gas quantities. The physically acting solvents known for this application are, e.g. Selexol, Morphysorb, Rectisol, etc.

The objective of the invention is to provide an improved solvent that combines the advantages of the chemically and physically acting absorbents and that permits particularly high loads.

The objective of the invention is achieved by the application of a liquid for removing sour gas components from technical gases, the said liquid containing the following substances:

-   -   0.1 to 100% by wt. of an amine or several amines in accordance         with the formula: H₂N—CH₂(CHR₂)_(x)—(OCH₂(CHR₃)_(y))₂—OR₁,         where:     -   R₁: C₁ to C₆alkyl     -   R₂: H or CH₃     -   R₃: H or CH₃     -   x: 0 to 3     -   y: 1 to 3     -   z: 0 to 10     -   0 to 99.9% of any other solvent, including water.         Provided the said liquid is circulated in a closed loop, it may         also contain solved residual components of the removed sour gas         components as well as impurities.

The technical gas loaded with sour gas components comes into contact with the said liquid, standard processes and devices being used for this purpose, such as scrubbing columns, membrane type contactors, spray-type scrubbers, etc. It is common practice to regenerate the loaded liquid in one or several steps, the steps primarily utilized serving for pressure reduction, temperature rise and stripping of the solution with the aid of a stripping agent in a column. The inventive liquid is well suited for this purpose and for the circulation in a closed loop operated in a continuous cycle. Upon removal of the sour gas components, the technical gas is regarded as purified and thus becomes available for further applications.

According to an embodiment of the invention, CH₃ (C₁ alkyl, methyl) is selected as R₁. In a further embodiment of the invention, x equals 1 and R₂ equals H. In accordance with a further embodiment, x equals 2 and R₂ equals H. In a further embodiment of the invention, y equals 1 and R₃ equals H. In accordance with a further embodiment, z is a value of 1 to 4, the value 1 being preferably selected.

In a further embodiment of the invention, in which CH₃ (C₁ alkyl, methyl) is selected as R₁, x=1 or 2, and R₂═H, 0 is selected as z. Further embodiments provide for the following variables: CH₃ (C₁ alkyl, methyl) selected as R₁, x equals 1 and R₂═CH₃. In further embodiments of the invention, the latter values are selected as follows: z=0 or y=1, R₃═CH₃ and z=1.

In accordance with a further embodiment, the component piperazine, also known under the name of diethylenediamine, is added to the said liquid, using a quantity of up to 10% by wt. Hence, the preferred liquid thus obtained complies with the formula H₂N—(CH₂)₂—O(CH₂)₂—OCH₃, which may be diluted with water or another solvent and contain up to 10% by wt. piperazine.

The benefits of the invention are outlined on the basis of a test of comparison and a load comparison shown in FIG. 1. It reflects the solubility Y of CO₂ versus the CO₂ partial pressure x in the technical gas. The unit of measure for Y is Ndm³/kg, CO₂ partial pressure x being indicated in terms of bar. The solution of H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ is designated as MDEGA in FIG. 1.

The solution investigated consisted of 85% by wt. of the H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ compound and 15% by wt. of the secondary amine bismethyl diethylene glycol amine and was tested for its solubility potential for sour gas components. In fact, the test series surprisingly revealed that a solution with as high a portion as 85% by wt. H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ and 15% by wt. bismethyl diethylene glycol amine possesses a CO₂ absorption capacity that exceeds by factor 4 that of a solution mainly consisting of bismethyl diethylene glycol amine, a fact that clearly confirms the importance of as high a portion of H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ as possible to achieve as high a sour gas absorption capacity as possible.

FIG. 1 shows the comparison of an 85% by wt. solution of H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ with a 50% by wt. MDEA solution, the latter being considered as the state-of-the-art solvent best suited for CO₂ removal. The test carried out at a CO₂ partial pressure of 0.2 to 2 bar furnished proof of a 30 to 50% higher CO₂ absorption, at 5 to 10 bar a 50% higher CO₂ absorption and at 20 bar CO₂ partial pressure, the CO₂ absorption was even higher, i.e. 75% for the 85% by wt. solution of H₂N—(CH₂)₂—O(CH₂)₂—OCH₃ compared to the 50% by wt. MDEA solution.

The inventive solvent also absorbs other sour gas components, such as H₂S, HCN, COS and mercaptans, which constitutes a further benefit of the present invention. 

1. Application of a liquid for removing sour gas components from technical gases, the said liquid containing the following substances: 0.1 to 100% by wt. of an amine or several amines in accordance with the following formula: H₂N—CH₂(CHR₂)_(x)—(OCH₂(CHR₃)_(y))_(z)—OR₁, where: R₁: C₁ to C₆alkyl R₂: H or CH₃ R₃: H or CH₃ x: 0 to 3 y: 1 to 3 z: 0 to 10 0 to 99.9% by wt. of any other solvent, including water.
 2. Application in accordance with claim 1, CH₃ being selected as R₁.
 3. Application in accordance with claims 1 or 2, 1 being selected as x and H as R₂.
 4. Application in accordance with claims 1 or 2, 2 being selected as x and H as R₂.
 5. Application in accordance with any of the preceding claims 1 to 4, 1 being selected as y and H as R₃.
 6. Application in accordance with any of the preceding claims 1 to 5, a value of 1 to 4 being selected as z.
 7. Application in accordance with claim 6, 1 being selected as z.
 8. Application in accordance with claims 3 or 4, 0 being selected as z.
 9. Application in accordance with claim 2, 1 being selected as x and CH₃ as R₂.
 10. Application in accordance with claim 9, 0 being selected as z.
 11. Application in accordance with claim 9, 1 being selected as y, CH₃ as R₃ and 1 as z.
 12. Application in accordance with any of the preceding claims 1 to 11, characterized in that at least a portion of the solvent selected at random consists of piperazine.
 13. Application in accordance with claim 12, characterized in that the portion of piperazine has a value ranging from 0.1 to 10% by wt.
 14. Liquid containing the following: 0.1 to 99.9% by wt. of an amine or several amines in accordance with the formula: H₂N—CH₂(CHR₂)_(x)—(OCH₂(CHR₃)_(y))_(z)—OR₁, where R₁: C₁ to C₆ alkyl R₂: H or CH₃ R₃: H or CH₃ x: 0 to 3 y: 0 to 3 z: 0 to 10 0.1 to 10% by wt. of piperazine 0 to 99.8% by wt. of any other solvent, including water. 